Spring systems for vortex suppression devices

ABSTRACT

A vortex-induced vibration (VIV) suppression system configured to accommodate a change in an underlying tubular diameter. The system including an encircling member dimensioned to at least partially encircle an underlying tubular. The encircling member may be, for example, a collar or a VIV suppression device such as a strake, or any other type of VIV suppression device. The system further including a band member dimensioned to encircle the encircling member and hold the encircling member around the underlying tubular at a desired axial position. A spring member may further be provided. The spring member may be positioned between the encircling member and the band member and dimensioned to contract in response to an increase in a diameter of the underlying tubular and expand in response to a decrease in a diameter of the underlying tubular such that the encircling member remains at the desired axial position.

CROSS-REFERENCE TO RELATED APPLICATION

The application claims the benefit of the earlier filing date of U.S.Provisional Patent Application No. 61/711,987, filed Oct. 10, 2012 andincorporated herein by reference.

BACKGROUND OF THE INVENTION

A difficult obstacle associated with the exploration and production ofoil and gas is management of significant ocean currents. These currentscan produce vortex-induced vibration (VIV) and/or large deflections oftubulars associated with drilling and production. VIV can causesubstantial fatigue damage to the tubular or cause suspension ofdrilling due to increased deflections.

Two solutions for VIV suppression are helical strakes and fairings.Typically, helical strakes are made by installing fins helically arounda cylindrical shell. The cylindrical shell may be separated into twohalves and positioned around the tubular to helically arrange the finsaround the underlying tubular. While helical strakes, if properlydesigned, can reduce the VIV fatigue damage rate of a tubular in anocean current, they typically produce an increase in the drag on thetubular and hence an increase in deflection. Thus, helical strakes canbe effective for solving the vibration problem at the expense ofworsening the drag and deflection problem.

Another solution is to use fairings as the VIV suppression device.Typical fairings have a substantially triangular shape and work bystreamlining the current flow past the tubular. A properly designedfairing can reduce both the VIV and the drag. Fairings are usually madeto be free to weathervane around the tubular with changes in the oceancurrent.

A challenge associated with both helical strakes and fairings is theiruse on tubulars that have an outside diameter that shrinks due tohydrostatic pressure. This is often true of risers that have insulationor buoyancy on the outside of an inner metallic tubular. Since it isusually much cheaper to install helical strakes or fairings on a tubularwhile it is above the water surface (before it is lowered), this meansthat the tubular diameter will often be larger at the surface than atdepth. Helical strakes that are banded onto the tubular risk comingloose when the diameter shrinks since the bands are typically notsufficiently compliant to accommodate the diameter change. Fairingsutilize thrust collars that restrain the fairings from sliding down thetubular. These thrust collars are often banded on and suffer from thesame lack of compliance that helical strakes experience.

SUMMARY OF THE INVENTION

In accordance with an embodiment of the invention, a device forsupporting a vortex-induced vibration (VIV) suppression device isdisclosed. The device may include a collar member having a web portiondimensioned to encircle an underlying tubular and flanges extending fromopposing sides of the web portion in a direction opposite the underlyingtubular. A band member may be provided which encircles the web portionand the underlying tubular so as to hold the collar member about thetubular. A resilient member may be positioned between the collar memberand the web portion. The resilient member may be dimensioned to expandor contract in response to a change in diameter of the underlyingtubular so that an axial alignment of the collar member about theunderlying tubular can be maintained.

In accordance with another embodiment of the invention, a system forreducing vortex induced vibration (VIV) about a tubular is disclosed.The system may include a strake section having a shell portiondimensioned to encircle an underlying tubular and a fin extending fromthe shell portion. A slot may be formed through the fin portion and aband member dimensioned for insertion through the slot and around theshell portion may be provided. The system may further include aresilient member positioned within the slot portion, the resilientmember dimensioned to expand or contract in response to a change indiameter of the underlying tubular so that an axial alignment of thestrake section about the underlying tubular is maintained.

In accordance with another embodiment of the invention, a vortex-inducedvibration (VIV) suppression system configured to accommodate a change inan underlying tubular diameter is disclosed. The system may include anencircling member dimensioned to at least partially encircle anunderlying tubular. The encircling member may be, for example, a collaror a VIV suppression device such as a strake, or any other type of VIVsuppression device. The system may further include a band memberdimensioned to encircle the encircling member and hold the encirclingmember around the underlying tubular at a desired axial position. Aspring member may further be provided. The spring member may bepositioned between the encircling member and the band member anddimensioned to contract in response to an increase in a diameter of theunderlying tubular and expand in response to a decrease in a diameter ofthe underlying tubular such that the encircling member remains at thedesired axial position.

The above summary does not include an exhaustive list of all aspects ofthe present invention. It is contemplated that the invention includesall apparatuses that can be practiced from all suitable combinations ofthe various aspects summarized above, as well as those disclosed in theDetailed Description below and particularly pointed out in the claimsfiled with the application. Such combinations have particular advantagesnot specifically recited in the above summary.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments disclosed herein are illustrated by way of example andnot by way of limitation in the figures of the accompanying drawings inwhich like references indicate similar elements. It should be noted thatreferences to “an” or “one” embodiment in this disclosure are notnecessarily to the same embodiment, and they mean at least one.

FIG. 1A is a perspective view of one embodiment of a collar half.

FIG. 1B is an end view of one embodiment of a collar half with springs.

FIG. 1C is a cross sectional view of the collar half of b along lineA-A′.

FIG. 1D is a cross sectional view of the collar half of FIG. 1B alongline A-A′.

FIG. 1E illustrates the collar half of FIG. 1D coupled to a secondcollar half.

FIG. 1F illustrates a side view of one embodiment of a plurality ofsuppression devices supported along a tubular.

FIG. 2A is a side view of one embodiment of a helical strake on atubular with a spring.

FIG. 2B is a cross sectional end view of the helical strake of FIG. 2Aalong line B-B′.

FIG. 2C is a cross sectional view of the helical strake of FIG. 2B alongline C-C′.

FIG. 2D is a top view of one embodiment of a spring.

DETAILED DESCRIPTION OF THE INVENTION

In this section we shall explain several preferred embodiments withreference to the appended drawings. Whenever the shapes, relativepositions and other aspects of the parts described in the embodimentsare not clearly defined, the scope of the embodiments is not limitedonly to the parts shown, which are meant merely for the purpose ofillustration. Also, while numerous details are set forth, it isunderstood that some embodiments may be practiced without these details.In other instances, well-known structures and techniques have not beenshown in detail so as not to obscure the understanding of thisdescription.

The present invention is directed to a spring system that allows a band,or other structure, used to position a VIV suppression device about atubular to accommodate changes in the tubular outside diameter so that aposition of the VIV suppression device can be maintained. In someembodiments, the spring system is a discrete spring system made up ofmore than one spring member that can be positioned about the band. Ithas been found that, in some embodiments, a discrete spring system ispreferable over a system that runs most of the length of the band (e.g.,a resilient liner) because such a unitary system may not be able toaccommodate a significant amount of tubular shrinkage since the bandpressure is low relative to the material stiffness of most practicalliner materials. Even if such a spring system is hollow, it is difficultto obtain sufficient deformation of the liner so that it acts like aspring with low creep or compression set.

Referring now to the invention in more detail, FIG. 1A is a perspectiveview of one embodiment of a collar half. Collar half 101 may be half ofa collar used to axially align a VIV suppression device about a tubular.Collar half 101 may include a web 105 and two flanges 104. Web 105 maybe used as a surface to band the collar against a tubular or otherstructure. In this aspect, web 105 may be, for example, a band shapedmember have dimensions which conform to a curvature of an underlyingtubular or other structure. Flanges 104 may extend from opposing sidesof web 105 in a substantially perpendicular direction (away from anunderlying tubular) such that they can be used to restrict adjacentstructures, such as VIV suppression devices, from sliding past collarhalf 101. Collar half 101 may be made of any suitable materialincluding, but not limited to, thermoplastics, elastomers, metals, andcomposite or hybrid materials. Although a single collar half 101 isillustrated in FIG. 1A, it is to be understood that a complete collarincludes a second collar half which is substantially identical to collarhalf 101 such that when the two are used together, they encircle anentire circumference of the underlying tubular.

FIG. 1B illustrates an end view of a collar half such as thatillustrated in FIG. 1A. Representatively, collar half 101 is again shownhaving a web 105 and two flanges 104. Springs 103 are shown positionedin a widthwise direction across web 105. Springs 103 are shownpositioned directly on top of web 105 such that when bands 102 arewrapped around web 105, springs 103 are between web 105 and bands 102.In this aspect, when bands 102 are tightened, they apply pressure tosprings 103 which, in turn, causes springs 103 to deform. Springs 103apply pressure to web 105, which can then apply pressure to anunderlying structure (e.g., a tubular).

Still referring to FIG. 1B, web 105 will typically range from 1/2 inchwide to 12 inches wide, but most typically will range from 1 inch wideto 6 inches wide. A single band 102 may be used, or multiple bands 102may be used. The bands 102 will typically range in width from 1/2 inchto 2 inches.

Springs 103 may have a finite width and may, or may not, cover theentire distance between the two flanges 104 (i.e., a width of web 105).Springs 103 may be of any suitable size, but the total of all of thesprings 103 will typically cover no more than 1/2 of the totalcircumference of collar half 101. Springs 103 may be any type ofresilient structure, for example, a hollow structure, a solid structureor made of a solid material. Springs 103 may also consist of other typesof compression springs such as a coiled spring. Springs 103 may beattached to web 105 using any suitable attachment mechanism (e.g.,screws, bolts, brackets, adhesives, or the like) or may be positioned onweb 105 and held in place by flanges 104 and bands 102. Still further,in some embodiments, springs 103 may be molded to web 105 and/or one orboth of flanges 104 by any suitable molding technique.

Still referring to FIG. 1B, collar half 101 and springs 103 may be madeof any suitable material, including thermoplastics, elastomers, metals,and composite of hybrid materials. For example, springs 103 may be madeof stripes of an elastomeric material.

Referring to FIG. 1C, FIG. 1C illustrates a cross-sectional side view ofthe collar half of FIG. 1B along line A-A′ and positioned around anunderlying structure. In particular, collar half 101 is shown positionedaround tubular 100. Collar half 101 includes web 105 and flange 104extending therefrom. From this view, it can be seen that springs 103 arepositioned against web 104 and band 102 lies on top of springs 103. Notethat it is also possible for band 102 to go through one or more springs103. In this way, the springs may be pre-installed onto the bands.

Again referring to FIG. 1C, band 102 has a substantially fixed lengthsuch that once it is secured around collar half 101 and the underlyingtubular 101, band 102 has a substantially fixed circumference. Thus,when band 102 is put into tension (such as by an expansion of tubular101), it applies pressure to springs 103 which causes springs 103 tocompress to accommodate the diameter change. Similarly, when a tensionon band 102 is reduced (such as by a contracting tubular diameter),springs 103 expand to fill in the gap created between band 102 and thereduced tubular diameter so that collar half 101 is still held tightlyaround tubular 100.

It is noted that by having discrete springs instead of a continuousspring or liner, the local pressure on springs 103 is higher (for agiven band tension) and thus the compression of springs 103 is greater.This allows collar half 101 and band 102 to accommodate a greater changein the diameter of tubular 100 than a continuous spring or liner wouldallow.

Still referring to FIG. 1C, web 105 may be, for example, 1/8 of an inchthick to 1 inch thick but may be of any suitable thickness. Flanges 104may be of any suitable height. Springs 103 will be of the height andwidth required to accommodate the required change in diameter of tubular100, for example from about 1/4 inch to 2 inches tall.

FIG. 1D illustrates a cross-sectional side view of the collar half ofFIG. 1B along line A-A′, which is substantially similar to the collarhalf of FIG. 1C except in this embodiment, guides are included to helpholds springs in a desired position. From this view, it can be seen thatcollar half 101 may be substantially similar to the previously discussedcollar half in that it includes web 105 and flanges 104. Springs 103 canbe positioned against web 105 and band 102 lies on top of springs 103 aspreviously discussed. A tubular (not shown) lies underneath collar half101. Optional guides 106 are adjacent to one of the springs 103 to keepthe spring from sliding relative to web 105. Guides 106 may help toprevent springs 103 from sliding along web 105.

For example, in one embodiment, guides 106 may be provided on one ormore sides of spring 103 to provide resistance against sliding ofsprings 103. Guides 106 may be made of a single member or multiplestructural members and may be of any size and shape suitable forpreventing sliding of springs 103. For example, guides 106 may be “U”shaped brackets which extend between flanges 104 and along part of thespan of springs 103. Alternatively, guides 106 may be placed on top ofsprings 103. Or guides may be placed on, or under, or around band 102.In some embodiments, guides 106 may be fastened to collar half 101 byeither fastening to web 105 or to flanges 104 by any suitable mechanism(e.g., bolts, screws, bands, brackets, adhesive or the like). In stillfurther embodiments, guides 106 may also be fastened directly to springs103 or to band 102.

Guides 106 may be of any size and shape suitable for preventing slidingof springs 103 around web 105. Representatively, in one embodiment,guides 106 may be fastener such as a bolt or screw. Guides 106 may beused to hold up any suitable spring shape. For example, guides 106 maybe used to hold a helical compression spring in place. Although twoguides 106 are illustrated, it is contemplated that any number of guides106 may be used. For example, all of the springs 103 may have guides106, none of the springs 103 may have guides 106, or one or more of thesprings 103 may have guides 106. Guides 106 may also be consideredhousings dimensioned to house an associated spring.

FIG. 1E illustrates the collar half of FIG. 1D coupled to a secondcollar half. Representatively, it can be seen from this view that collarhalves 101A and 101B are held onto a tubular by band 102. Collar halves101A and 102B have webs 105A and 105B as well as flanges 104A and 104B,respectively. Springs 103 reside under band 102 and optional guides 106restrain one or more springs 103 from sliding or overturning.

Again referring to FIG. 1E, this figure illustrates that either one ortwo collar halves may be used. Also, collars whose sum of all of theirsegments does not cover the full circumference may be used, and anynumber of segments may be used to make up the collar. Any number ofsprings 103 may also be used and any number of these springs 103 may, ormay not, have one or more guides 106. Collar halves 101A and 101B may besecured together around the tubular by band 102, or/or by other securingmechanisms (e.g., a hinge).

FIG. 1F illustrates a side view of suppression devices held in placealong an underlying structure by any one or more of the previouslydiscussed collar halves. In particular, as can be seen from this view,collar halves 101 are positioned between ends of suppression devices 108such that they prevent suppression devices 108 from sliding axiallyalong the underlying structure 100 (e.g., a tubular). In one embodiment,suppression devices 108 may be fairings free to weathervane around thetubular 100 while collar halves 101 are clamped around the underlyingthe tubular.

FIG. 1F illustrates an embodiment in which each of collar halves 101support two suppression devices 108. It is contemplated, however, thatcollar halves 101 can support any number of suppression devices 108ranging from 1 to 100, for example where suppression devices 108 arefairings, each of collar halves 101 can support between 1 and 8fairings. Collar halves 101 may also support other suppression devicessuch as helical strakes, Henning devices, splitter plate type devices,smooth sleeves, perforated structures, or any other device that requiressupport on a tubular.

FIG. 2A illustrates a side perspective view of one embodiment of asuppression device positioned around an underlying structure.Representatively, FIG. 2A shows helical strake section 201 positionedaround tubular 200. Strake section 201 may have three fins 202 that areattached to, or part of, shell 203. A slot 204 may be formed through oneor more of fins 202. A spring 205 for accommodating a tubular diameterchange, such as any of those previously discussed, may be positionedwithin slot 204. Optional fasteners 210 may assist in keeping spring 205in place, either directly or by restraining an internal structure.

Helical strake section 201 may be a single piece or may consist of twoor more sections around the circumference. Any number of fins 202 and/orslots 204 and/or springs 205 may be present. Each fin may or may nothave one or more slots, and each slot may or may not have one or moresprings. In this aspect, when a band (not shown) is placed aroundhelical strake section 201, through slot 204 and on top of spring 205,spring 205 compresses as the band tightens. If a diameter of tubular 200shrinks or otherwise changes, the spring allows the band to maintaintension even though the diameter changes. Bands may be placed on top ofspring 205 or may go through spring 205. Also, the band may reside in achannel, such as a channel to produce a gap or stand-off between themain strake body from the underlying tubular.

Spring 205 may be of any suitable shape but will typically fit into partof slot 204 and/or fins 202. Spring 205 may be of any suitable height,and of any suitable cross section or even spring type. The helical shapeof the fins 202 may sufficiently keep springs 205 in place. Optionalfasteners 210 for keeping spring 205 in place my further be provided.Fasteners 210 may be any type of fastener of any size suitable forretaining spring 205 within slot 204. For example, fasteners 210 may bebolts, screws, brackets, adhesives or the like. Helical strake section201, including fins 202, shell 203, and spring 205, may be made of anysuitable material such as those previously discussed.

FIG. 2B illustrates a cross-sectional view of the helical strake sectionof FIG. 2A along line B-B′. FIG. 2B shows helical strake section 201having shell halves 203A and 203B which are banded together using band207. Shell halves 203A and 203B meet at a gap 206, which may in someembodiments, extend along a length of fin 202. Helical strake section201 has fins 202 that are attached to shell half 203A or shell half203B. Springs 205 are shown positioned through slots within each of thefins 202. In this aspect, when band 207 is put into tension, itcompresses springs 205 and puts pressure onto shell halves 203A and 203Bwhich, in turn put pressure on an inner tubular (not shown). Gap 206 mayget smaller as the band tension is increased.

Springs 205 may be of any suitable size, shape, material, or type suchas those previously discussed, provided they are able to compress whenband 207 is tightened. Springs 205 will typically each cover less than20% of the helical strake section 201 circumference. The total ofsprings 205, for a give point along the length of strake section 201,will cover less than 50% of the circumference of strake section 201.

FIG. 2C illustrates a cross-sectional view of the helical strake sectionof FIG. 2B along line C-C′. From this view, it can be seen that fin 202includes a first portion 202A and a second portion 202B which extendfrom shell 203 such that a hollow channel 212 is formed within fin 202.In this aspect, slot 204 is formed through both of the first portion202A and second portion 202B such that spring 205 and band 207 gothrough both sides of fin 202. Band 207 is positioned on top of spring205. In some embodiments, spring 205 may include a middle portion 208which rests within hollow channel 212 and is dimensioned to keep thespring from slipping out through the slot. For example, middle portion208 may extend out of the plane such that it is wider than slot 204, andin some cases, is wider than opposing ends of spring 205. In thisaspect, when the tension of band 207 is increased, spring 205 compressesonto shell 203. Spring section 208, which is part of spring 205, will inturn partially compress.

FIG. 2D illustrates a top view of the spring of FIG. 2C. From this view,it can be seen that spring 205 includes middle portion 208 which iswider than the rest of spring 205 and wider than the slot within whichspring 205 is inserted. With middle portion 208, spring 205 isintentionally and significantly wider than a slot that spring 205 wouldbe inserted into. In this fashion, middle portion 208 assist in keepingspring 205 in place and from sliding through the slot and out of theslot.

Although a spring having a wider middle portion 208 is shown, it iscontemplated that in other embodiments, fasteners or other appurtenancesmay be used in place of middle portion 208. Middle portion 208 may bemade of any suitable size, shape and material. Middle portion 208 may bepart of spring 205 or middle portion 208 may be separate pieces that arebonded or attached to spring 205.

In the foregoing specification, the invention has been described withreference to specific embodiments thereof. It will, however, be evidentthat various modifications and changes can be made thereto withoutdeparting from the broader spirit and scope of the invention as setforth in the appended claims. For example, while discrete springs for acollar and for a helical strake are shown, the spring system disclosedherein may be used for other structures that may be attached to atubular such as Henning devices or measurement clamps. The discretesprings may also be used for a banded or bolted device (e.g. collar, orhelical strake) by placing them between the device and the tubular. Thesprings may be put underneath the device so that the springs are locatedbetween the device and the tubular. The specification and drawings are,accordingly, to be regarded in an illustrative rather than a restrictivesense.

What is claimed is
 1. A system for reducing vortex induced vibration(VIV) about a tubular, the system comprising: a strake section having ashell portion dimensioned to encircle an underlying tubular and a finextending from the shell portion; a slot formed through the fin portion;a band member dimensioned for insertion through the slot and around theshell portion; and a resilient member positioned around the shellportion, the resilient member having discrete sections that are spacedapart and dimensioned to expand or contract in response to a change indiameter of the underlying tubular so that an axial alignment of thestrake section about the underlying tubular is maintained, each of thediscrete sections being positioned at an opening formed through theshell portion such that a portion of each of the discrete sections isexposed through the shell portion to an underlying tubular.
 2. Thesystem of claim 1 wherein the resilient member is positioned between theband member and the shell portion, and at least one of the discretesections is positioned collinear with the fin portion.
 3. The system ofclaim 1 wherein the fin portion comprises a first portion and a secondportion and the opening is formed through a section of the shell portionbetween the first portion and the second portion.
 4. The system of claim3 wherein the slot is formed through the first portion and the secondportion of the fin, and the resilient member comprises end portions anda middle portion, wherein the ends portions extend through the slotformed in the first portion and the second portion and the middleportion is aligned with the opening.
 5. The system of claim 1 whereineach of the discrete sections is dimensioned to encircle less than 20%of the circumference of the strake section.
 6. The system of claim 1wherein for a given point along a length of the strake section, thediscrete sections combined, encircle less than 50% of the circumferenceof the strake section.
 7. A vortex-induced vibration (VIV) suppressionsystem configured to accommodate a change in an underlying tubulardiameter, the system comprising: an encircling member dimensioned to atleast partially encircle an underlying tubular; a band memberdimensioned to encircle the encircling member and hold the encirclingmember around the underlying tubular at a desired axial position; and aspring member positioned between the encircling member and the bandmember, wherein the spring member comprises spaced apart sections thatare dimensioned to encircle less than half of a full circumference ofthe encircling member and to contract in response to an increase in adiameter of the underlying tubular and expand in response to a decreasein a diameter of the underlying tubular such that the encircling memberremains at the desired axial position.
 8. The system of claim 7 whereinthe encircling member is a collar configured to be positioned at an endof a VIV suppression device.
 9. The system of claim 7 wherein theencircling member is a shell portion of a helical strake.
 10. The systemof claim 7 wherein the spring member is positioned within the encirclingmember.